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INA118
SBOS027B – SEPTEMBER 2000 – REVISED APRIL 2019
INA118 Precision, Low-Power Instrumentation Amplifier
A newer version of this device is now available: INA818
1 Features
3 Description
•
The INA118 is a low-power, general-purpose
instrumentation amplifier offering excellent accuracy.
The versatile, three op amp design and small size
make this device an excellent choice for a wide range
of applications. Current-feedback input circuitry
provides wide bandwidth, even at high gain (70 kHz
at G = 100).
1
•
•
•
•
•
•
•
•
A newer version of this device is now available:
INA818
Low offset voltage: 50 µV, maximum
Low drift: 0.5 µV/°C, maximum
Low input bias current: 5 nA, maximum
High CMR: 110 dB, minimum
Inputs protected to ±40 V
Wide supply range: ±1.35 to ±18 V
Low quiescent current: 350 µA
Packages: 8-Pin plastic DIP, SO-8
A single external resistor sets any gain from 1 to
10000. Internal input protection can withstand up to
±40 V without damage.
The INA118 is laser-trimmed for low offset voltage
(50 µV), drift (0.5 µV/°C), and high common-mode
rejection (110 dB at G = 1000). The INA118 operates
with power supplies as low as ±1.35 V, and quiescent
current is only 350 µA, making this device an
excellent choice for battery-operated systems.
2 Applications
•
•
•
•
•
Bridge amplifiers
Thermocouple amplifiers
RTD Sensor amplifiers
Medical instrumentation
Data acquisition
The INA118 is available in 8-pin plastic DIP and SO-8
surface-mount packages, and specified for the –40°C
to +85°C temperature range.
The upgraded INA818 offers a lower input stage
offset voltage (35 µV, maximum), lower input bias
current (0.5 nA maximum) and lower noise (8
nV/√Hz) at the same quiescent current. See the
Device Comparison Table for a selection of precision
instrumentation amplifiers from Texas Instruments.
Device Information(1)
PART NUMBER
INA118
PACKAGE
BODY SIZE (NOM)
SOIC (8)
3.91 mm × 4.90 mm
PDIP (8)
6.35 mm × 9.81 mm
(1) For all available packages, see the package option addendum
at the end of the data sheet.
Simplified Schematic
V+
7
2
–
VIN
Over-Voltage
Protection
INA118
A1
60kΩ
1
G=1+
60kΩ
50kΩ
RG
25kΩ
A3
RG
8
+
VIN
3
6
VO
25kΩ
Over-Voltage
Protection
5
A2
60kΩ
Ref
60kΩ
4
V–
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
A newer version of this device is now available: INA818
INA118
SBOS027B – SEPTEMBER 2000 – REVISED APRIL 2019
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Comparison Table.....................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
5
7.1
7.2
7.3
7.4
7.5
7.6
5
5
5
5
6
8
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 12
8.1
8.2
8.3
8.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
12
12
13
13
9
Application and Implementation ........................ 14
9.1 Application Information............................................ 14
9.2 Typical Application ................................................. 14
10 Power Supply Recommendations ..................... 18
10.1 Low-Voltage Operation ......................................... 18
10.2 Single-Supply Operation ....................................... 19
11 Layout................................................................... 20
11.1 Layout Guidelines ................................................. 20
11.2 Layout Example .................................................... 21
12 Device and Documentation Support ................. 22
12.1
12.2
12.3
12.4
12.5
12.6
Device Support ....................................................
Documentation Support ........................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
22
22
22
22
22
22
13 Mechanical, Packaging, and Orderable
Information ........................................................... 22
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (January 2016) to Revision B
Page
•
Added information about the newer, upgraded INA818 ........................................................................................................ 1
•
Added Device Comparison Table........................................................................................................................................... 3
Changes from Original (September 2000) to Revision A
•
2
Page
Added ESD Ratings table, Feature Description section, Device Functional Modes section, Application and
Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation
Support section, and Mechanical, Packaging, and Orderable Information section. .............................................................. 1
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SBOS027B – SEPTEMBER 2000 – REVISED APRIL 2019
5 Device Comparison Table
DEVICE
GAIN EQUATION
RG PINS AT PIN
INA818
35-µV Offset, 0.4 µV/°C VOS Drift, 8-nV/√Hz Noise, Low-Power,
Precision Instrumentation Amplifier
DESCRIPTION
G = 1 + 50 kΩ / RG
1, 8
INA819
35-µV Offset, 0.4 µV/°C VOS Drift, 8-nV/√Hz Noise, Low-Power,
Precision Instrumentation Amplifier
G = 1 + 50 kΩ / RG
2, 3
INA821
35-µV Offset, 0.4 µV/°C VOS Drift, 7-nV/√Hz Noise, HighBandwidth, Precision Instrumentation Amplifier
G = 1 + 49.4 kΩ / RG
2, 3
INA828
50-µV Offset, 0.5 µV/°C VOS Drift, 7-nV/√Hz Noise, Low-Power,
Precision Instrumentation Amplifier
G = 1 + 50 kΩ / RG
1, 8
INA333
25-µV VOS, 0.1 µV/°C VOS Drift, 1.8-V to 5-V, RRO, 50-µA IQ,
chopper-stabilized INA
G = 1 + 100 kΩ / RG
1, 8
PGA280
20-mV to ±10-V Programmable Gain IA With 3-V or 5-V
Differential Output; Analog Supply up to ±18 V
Digital programmable
N/A
INA159
G = 0.2 V Differential Amplifier for ±10-V to 3-V and 5-V
Conversion
G = 0.2 V/V
N/A
PGA112
Precision Programmable Gain Op Amp With SPI
Digital programmable
N/A
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SBOS027B – SEPTEMBER 2000 – REVISED APRIL 2019
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6 Pin Configuration and Functions
P and D Packages
8-Pin PDIP and SOIC
Top View
RG
1
8
RG
V–IN
2
7
V+
+
IN
3
6
VO
V–
4
5
Ref
V
Pin Functions
PIN
NO.
NAME
I/O
DESCRIPTION
1
RG
—
2
V–IN
I
Negative input
3
+
I
Positive input
V
IN
Gain setting pin. For gains greater than 1, place a gain resistor between pin 1 and pin 8.
4
V–
—
5
Ref
I
Reference input. This pin must be driven by low impedance or connected to ground.
6
VO
O
Output
7
V+
—
Positive supply
8
RG
—
Gain setting pin. For gains greater than 1, place a gain resistor between pin 1 and pin 8.
4
Negative supply
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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
±18
V
±40
V
125
°C
Junction temperature
150
°C
Lead temperature (soldering, 10 s)
300
°C
125
°C
Supply voltage
Analog input voltage
Output short-circuit (to ground)
Continuous
Operating temperature
Tstg
(1)
–40
Storage temperature
–40
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±1000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
V
Power supply
VO = 0
Input common-mode voltage
TA
Ambient temperature
MIN
NOM
MAX
UNIT
±2.25
±15
±18
V
V– + 1.1
V+ – 1
V
–55
150
°C
7.4 Thermal Information
INA118
THERMAL METRIC (1)
D (SOIC)
P (PDIP)
8 PINS
8 PINS
UNIT
RθJA
Junction-to-ambient thermal resistance
115
48
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
62
37
°C/W
RθJB
Junction-to-board thermal resistance
59
25
°C/W
ψJT
Junction-to-top characterization parameter
14
14
°C/W
ψJB
Junction-to-board characterization parameter
58
25
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
N/A
N/A
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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7.5 Electrical Characteristics
at TA = 25°C, VS = ±15 V, and RL = 10 kΩ (unless otherwise noted_
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
INPUT
Offset voltage, RTI
Initial
TA = 25°C
vs Temperature
TA = TMIN to TMAX
vs Power supply
VS = ±1.35 V to ±18 V
INA118PB, UB
±10 ± 50/G
±50 ± 500/G
INA118P, U
±25 ±100/G
±125±1000/G
INA118PB, UB
±0.2 ± 2/G
±0.5 ± 20/G
INA118P, U
±0.2 ± 5/G
±1 ± 20/G
INA118PB, UB
±1 ±10/G
±5 ± 100/G
INA118P, U
±1 ±10/G
±10 ±100/G
Long-term stability
±0.4 ±5/G
10
Differential
10
Common-mode
1010 || 4
Impedance
Linear input voltage range
(V+) – 0.65
–
(V ) + 1.1
(V–) + 0.95
90
Safe input voltage
INA118PB, UB
80
INA118P, U
73
90
VCM = ±10 V, ΔRS = 1 kΩ,
G = 10
INA118PB, UB
97
110
VCM = ±10 V, ΔRS = 1 kΩ,
G = 100
INA118PB, UB
VCM = ±10 V, ΔRS = 1 kΩ,
G = 1000
INA118PB, UB
INA118P, U
100
125
Common-mode rejection
Bias current
INA118P, U
INA118P, U
89
110
107
120
98
120
110
125
±1
±5
INA118P, U
±1
±10
±1
±5
INA118P, U
±1
±10
f = 10 Hz
f = 100 Hz
f = 1 kHz
G = 1000, RS = 0 Ω
fB = 0.1 Hz to 10 Hz
Noise current
nA
pA/°C
INA118PB, UB
vs Temperature
V
dB
±40
Offset current
Noise voltage, RTI
V
INA118PB, UB
vs Temperature
µV/V
Ω || pF
±40
VCM = ±10 V, ΔRS = 1 kΩ,
G=1
µV/°C
µV/mo
|| 1
(V+) – 1
µV
nA
±40
pA/°C
11
nV/√Hz
10
nV/√Hz
10
nV/√Hz
0.28
µVp-p
f = 10 Hz
2
f = 1 kHz
0.3
fB = 0.1 Hz to 10 Hz
80
pA/√Hz
pAp-p
GAIN
Gain equation
1 + (50 kΩ/RG)
Range of gain
Gain error
Gain vs temperature
1
G=1
±0.01%
±0.024%
G = 10
±0.02%
±0.4%
G = 100
±0.05%
±0.5%
G = 1000
±0.5%
±1%
G=1
(1)
6
V/V
±1
±10
ppm/°C
±25
±100
ppm/°C
G=1
±0.0003
±0.001
G = 10
±0.0005
±0.002
G = 100
±0.0005
±0.002
G = 1000
±0.002
±0.01
50-kΩ resistance (1)
Nonlinearity
V/V
10000
% of FSR
Temperature coefficient of the 50-kΩ term in the gain equation.
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Electrical Characteristics (continued)
at TA = 25°C, VS = ±15 V, and RL = 10 kΩ (unless otherwise noted_
PARAMETER
TEST CONDITIONS
MIN
TYP
(V+) – 1
(V+) – 0.8
(V ) + 0.35
(V–) + 0.2
MAX
UNIT
OUTPUT
Positive
Voltage:
Negative
Single supply high
Single supply low
RL = 10 kΩ
–
VS = 2.7 V/0 V (2), RL = 10 kΩ
1.8
2
60
35
Load capacitance stability
Short circuit current
V
mV
1000
pF
+5/–12
mA
FREQUENCY RESPONSE
Bandwidth, –3 dB
G=1
800
G = 10
500
G = 100
70
G = 1000
Slew rate
Settling time, 0.01%
Overload recovery
kHz
7
VO = ±10 V, G = 10
0.9
G=1
15
G = 10
15
G = 100
21
G = 1000
210
50% Overdrive
V/µs
µs
20
µs
POWER SUPPLY
Voltage range
Current
±1.35
VIN = 0 V
±15
±18
V
±350
±385
µA
TEMPERATURE RANGE
Specification
–40
85
°C
Operating
–40
125
°C
(2)
Common-mode input voltage range is limited. See text for discussion of low power supply and single power supply operation.
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7.6 Typical Characteristics
at TA = 25°C, VS = ±15 V (unless otherwise noted)
140
60
G = 1000
Gain (dB)
40
Common-Mode Rejection (dB)
50
G = 100
30
20
G = 10
10
0
G=1
–10
120
G=1000
100
G=100
80
G=10
60
G=1
40
20
0
–20
1k
10k
100k
1M
1
10M
10
100
Figure 1. Gain vs Frequency
G ‡ 10
10
G=1
G=1
5
VD/2
VD/2
–5
+
–
–15
–15
VO
INA118
Ref
+
VCM
–10
+15V
–
–15V
All
Gains
–10
All
Gains
–5
0
5
G=1
2
15
G=1
+5V
1
VD/2
0
VD/2
–1
–
+
–
VO
INA118
Ref
+
VCM
–2
–5V
–3
–5
–5
All
Gains
–4
–3
All
Gains
–2
–1
0
1
2
3
4
5
Output Voltage (V)
Output Voltage (V)
Figure 3. Input Common-Mode Range vs Output Voltage
Figure 4. Input Common-Mode Range vs Output Voltage
3
G ‡ 10
4
G=2
3
G=1
Single Supply
2
+5V
VD/2
VD/2
1
–
+
–
VO
INA118
Ref
+
Common-Mode Voltage (V)
5
Common-Mode Voltage (V)
3
–4
10
G ‡ 10
G ‡ 10
4
Common-Mode Voltage (V)
Common-Mode Voltage (V)
G ‡ 10
0
100k
Figure 2. Common-Mode Rejection vs Frequency
5
15
G ‡ 10
2
G=1
Single Supply
+3V
VD/2
1
VD/2
–
+
–
+
VO
INA118
Ref
VCM
VCM
0
0
0
8
10k
1k
Frequency (Hz)
Frequency (Hz)
1
2
3
4
5
0
1
2
3
Output Voltage (V)
Output Voltage (V)
Figure 5. Input Common-Mode Range vs Output Voltage
Figure 6. Input Common-Mode Range vs Output Voltage
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Typical Characteristics (continued)
160
160
140
140
120
100
G = 1000
80
G = 100
60
G = 10
40
G = 1000
Power Supply Rejection (dB)
Power Supply Rejection (dB)
at TA = 25°C, VS = ±15 V (unless otherwise noted)
G=1
120
G = 100
100
G = 10
80
G=1
60
40
20
20
0
0
1
10
100
1k
10k
10
100k
100
1k
100
10
G = 10
G = 100, 1000
G = 1000 BW Limit
1
Current Noise
(All Gains)
1
10
100
Figure 8. Negative Power Supply Rejection vs Frequency
Settling Time (µs)
G=1
100
1
100k
1000
Input Bias Current Noise (pA/√ Hz)
Input-Referred Noise Voltage (nV/√ Hz)
Figure 7. Positive Power Supply Rejection vs Frequency
1k
10
10k
Frequency (Hz)
Frequency (Hz)
RL = 10kΩ
CL = 100pF
100
0.1%
0.1
1k
0.01%
10
10k
1
10
100
1000
Gain (V/V)
Frequency (Hz)
Figure 9. Input-Referred Noise Voltage vs Frequency
500
Figure 10. Settling Time vs Gain
1.5
10
S
400
IQ
1
VS = ±15V
300
0.5
VS = ±1.35V
Input Bias Current (mA)
ate
lew R
Slew Rate (V/µs)
Quiescent Current (µA)
8
6
4
2
G = 1000
G=1
0
–2
G=1
–4
G = 1000
–6
–8
200
–75
–50
–25
0
25
50
75
100
0
125
–10
–40
0
40
Overload Voltage (V)
Temperature (°C)
Figure 11. Quiescent Current and Slew Rate vs Temperature
Figure 12. Input Bias Current vs Input Overload Voltage
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V (unless otherwise noted)
5
Input Bias and Offset Current (nA)
10
Offset Voltage Change (µV)
8
6
4
G = 1000
2
0
–2
–4
–6
–8
–10
1.0
0.5
0
IOS
3
2
±I b
1
0
–1
–2
–3
–4
–5
3.0
2.5
2.0
1.5
4
–75
–50
–25
0
Time from Power Supply Turn On (ms)
Figure 13. Offset Voltage vs Warm-Up Time
Output Voltage Swing (V)
Output Voltage Swing (V)
Positive
VS £ ±5V
(V+) –0.8
VS = ±15V
(V–)+0.8
Single Power Supply, V– = 0V
Ground-Referred Load
(V–)+0.4
Negative
V+
(V+) –0.2
(V+) –0.4
(V+) –0.6
(V+) –0.8
(V+) –1
100
125
+85°C
+25°C
–40°C
RL = 10kΩ
+85°C
Negative
+25°C
(V–) +0.2
–40°C
V–
0
1
2
3
4
0
±5
Output Current (mA)
10
8
6
+|ICL|
2
0
Peak-to-Peak Output Voltage (V)
–|ICL|
12
4
±15
±20
Figure 16. Output Voltage Swing vs Power Supply Voltage
16
14
±10
Power Supply Voltage (V)
Figure 15. Output Voltage Swing vs Output Current
Short Circuit Current (mA)
75
Positive
(V–) +0.4
V–
32
G = 10, 100
28
G=1
24
20
16
G = 1000
12
8
4
0
–75
10
50
Figure 14. Input Bias and Offset Current vs Temperature
V+
(V+) –0.4
25
Temperature (°C)
–50
–25
0
25
50
75
100
125
100
1k
10k
100k
1M
Temperature (°C)
Frequency (Hz)
Figure 17. Output Current Limit vs Temperature
Figure 18. Maximum Output Swing vs Frequency
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V (unless otherwise noted)
1
THD + N (%)
G = 10
0.1
RL
=1
0k
Ω
0.1µV/div
0.01
RL = ∞
(Noise Floor)
0.001
20
100
1k
10k
20k
1s/div
Frequency (Hz)
Figure 19. THD + N vs Frequency
Figure 20. Input-Referred Noise, 0.1 Hz to 10 Hz
G=1
G = 100
20mV/div
G = 10
20mV/div
G = 1000
10µs/div
100µs/div
\
Figure 22. Small-Signal Response
Figure 21. Small-Signal Response
G=1
G = 100
5V/div
5V/div
G = 1000
G = 10
100µs/div
100µs/div
Figure 23. Large-Signal Response
Figure 24. Large-Signal Response
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8 Detailed Description
8.1 Overview
Figure 25 shows a simplified representation of the INA118 and provides insight into its operation. Each input is
protected by two FET transistors that provide a low series resistance under normal signal conditions, preserving
excellent noise performance. When excessive voltage is applied, these transistors limit input current to
approximately 1.5 to 5 mA.
The differential input voltage is buffered by Q1 and Q2 and impressed across RG, causing a signal current to flow
through RG, R1 and R2. The output difference amp, A3, removes the common-mode component of the input
signal and refers the output signal to the Ref terminal.
The equations in Figure 25 describe the output voltages of A1 and A2. The VBE and IR drop across R1 and R2
produce output voltages on A1 and A2 that are approximately 1-V lower than the input voltages.
8.2 Functional Block Diagram
A1 Out = VCM – VBE – (10µA • 25kΩ) – V O/2
A2 Out = VCM – VBE – (10µA • 25kΩ) + V O/2
Output Swing Range A 1, A 2; (V+) – 0.65V to (V–) + 0.06V
Amplifier Linear Input Range: (V+) – 0.65V to (V–) + 0.98V
10µA
VB
10µA
+
–
VO = G • (VIN – VIN)
Input Bias Current
Compensation
Output Swing Range:
(V+) – 0.8V to (V–) + 0.35V
A2
A1
C1
C2
60kΩ
60kΩ
60kΩ
A3
VO
60kΩ
–
VIN
Ref
Q1
R1
25kΩ
R2
25kΩ
Q2
RG
VD/2
(External)
VCM
VD/2
+
VIN
Figure 25. INA118 Simplified Circuit Diagram
12
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8.3 Feature Description
The INA118 input sections use junction field effect transistors (JFET) connected to provide protection up to
±40 V. The current-feedback architecture provides maximum bandwidth over the full range of gain settings.
8.4 Device Functional Modes
8.4.1 Noise Performance
The INA118 provides low noise in most applications. For differential source impedances less than 1 kΩ, the
INA103 may provide lower noise. For source impedances greater than 50 kΩ, the INA111 FET-Input
Instrumentation Amplifier may provide lower noise.
Low-frequency noise of the INA118 is approximately 0.28 µVp-p, measured from 0.1 to 10 Hz (G≥100). This
provides dramatically improved noise when compared to state-of-the-art chopper-stabilized amplifiers.
8.4.2 Input Common-Mode Range
The linear input voltage range of the input circuitry of the INA118 is from approximately 0.6-V less than the
positive supply voltage to 1-V greater than the negative supply. As a differential input voltage causes the output
voltage to increase, however, the linear input range is limited by the output voltage swing of amplifiers A1 and A2.
Thus, the linear common-mode input range is related to the output voltage of the complete amplifier. This
behavior also depends on supply voltage; see Figure 6.
Input-overload can produce an output voltage that appears normal. For example, if an input overload condition
drives both input amplifiers to their positive output swing limit, the difference voltage measured by the output
amplifier is near zero. The output of the INA118 is near 0 V even though both inputs are overloaded.
8.4.3 Input Protection
The inputs of the INA118 are individually protected for voltages up to ±40 V. For example, a condition of –40 V
on one input and +40 V on the other input does not cause damage. Internal circuitry on each input provides low
series impedance under normal signal conditions. To provide equivalent protection, series input resistors would
contribute excessive noise. If the input is overloaded, the protection circuitry limits the input current to a safe
value of approximately 1.5 to 5 mA. Figure 12 shows this input current limit behavior. The inputs are protected
even if the power supplies are disconnected or turned off.
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The INA118 measures a small differential voltage with a high common-mode voltage developed between the
noninverting and inverting input. The high common-mode rejection makes the INA118 suitable for a wide range
of applications. The ability to set the reference pin to adjust the functionality of the output signal offers additional
flexibility that is practical for multiple configurations
9.2 Typical Application
Figure 26 shows the basic connections required for operation of the INA118. Applications with noisy or high
impedance power supplies may require decoupling capacitors close to the device pins as shown. The output is
referred to the output reference (Ref) terminal, which is normally grounded. This must be a low-impedance
connection to assure good common-mode rejection. A resistance of 12 Ω in series with the Ref pin causes a
typical device to degrade to approximately 80-dB CMR (G = 1).
Figure 26 depicts an input signal with a 5-mV, 1-kHz signal with a 1-Vp-p common-mode signal, a condition often
observed in process control systems. Figure 27 depicts the output of the INA118 (gain = 250) depicting the clean
recovered 1-kHz waveform.
V+
0.1µF
7
–
VIN
DESIRED
GAIN
RG
( Ω)
NEAREST 1% RG
(Ω)
1
2
5
10
20
50
100
200
500
1000
2000
5000
10000
NC
50.00k
12.50k
5.556k
2.632k
1.02k
505.1
251.3
100.2
50.05
25.01
10.00
5.001
NC
49.9k
12.4k
5.62k
2.61k
1.02k
511
249
100
49.9
24.9
10
4.99
2
INA118
Over-Voltage
Protection
A1
W
60kΩ
1
+
–
)
VO = G • (VIN – VIN
60kΩ
25kΩ
G=1+
A3
RG
3
6
+
8
+
VIN
50kΩ
RG
25kΩ
Load VO
5
A2
Over-Voltage
Protection
60kΩ
4
60kΩ
–
Ref
0.1µF
NC: No Connection.
V–
Also drawn in simplified form:
–
VIN
RG
+
VIN
INA118
VO
Ref
Figure 26. Basic Connections
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Typical Application (continued)
9.2.1 Design Requirements
Figure 30 and Figure 29 depict the performance of a typical application of the INA118 in a shop floor vibration
sensing application. Because industrial process control systems often involve the interconnecting of multiple
subsystems, ground loops are frequently encountered and often are not easily solved. The inherent commonmode rejection of instrumentation amplifiers enables accurate measurements even in the presence of ground
loop potentials.
The typical application was tested in a system with these requirements:
• Transducer signal ≈ 5 mVp-p
• Transducer center frequency = 1 kHz
• Common-Mode signal (required to be rejected): 1 Vp-p at 60 Hz
9.2.2 Detailed Design Procedure
9.2.2.1 Setting the Gain
As shown in Equation 1, the gain of the INA118 is set by connecting a single external resistor, RG, connected
between pins 1 and 8.
50kΩ
G=1+
RG
(1)
Commonly used gains and resistor values are shown in Figure 26.
The 50-kΩ term in Equation 1 comes from the sum of the two internal feedback resistors of A1 and A2. These onchip metal film resistors are laser-trimmed to accurate absolute values. The accuracy and temperature coefficient
of these resistors are included in the gain accuracy and drift specifications of the INA118.
The stability and temperature drift of the external gain setting resistor, RG, also affects gain. The contribution of
RG to gain accuracy and drift can be directly inferred from Equation 1. Low resistor values required for high gain
can make wiring resistance important. Sockets add to the wiring resistance, which contributes additional gain
error (possibly an unstable gain error) in gains of approximately 100 or greater.
9.2.2.2 Dynamic Performance
The Figure 1 shows that, despite its low quiescent current, the INA118 achieves wide bandwidth, even at high
gain. This is due to the current-feedback topology of the INA118. Settling time also remains excellent at high
gain.
The INA118 exhibits approximately 3-dB peaking at 500 kHz in unity gain. This is a result of its current-feedback
topology and is not an indication of instability. Unlike an op amp with poor phase margin, the rise in response is a
predictable 6-dB/octave due to a response zero. A simple pole at 300 kHz or lower produces a flat passband
unity gain response.
9.2.2.3 Offset Trimming
The INA118 is laser-trimmed for low offset voltage and drift. Most applications require no external offset
adjustment. Figure 27 shows an optional circuit for trimming the output offset voltage. The voltage applied to the
Ref terminal is summed at the output. The op amp buffer provides low impedance at the Ref terminal to preserve
good common-mode rejection.
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Typical Application (continued)
–
VIN
V+
RG
INA118
VO
100µA
1/2 REF200
Ref
+
VIN
OPA177
±10mV
Adjustment Range
100Ω
10kΩ
100Ω
100µA
1/2 REF200
V–
Figure 27. Optional Trimming of Output Offset Voltage
9.2.2.4 Input Bias Current Return Path
The input impedance of the INA118 is extremely high at approximately 1010 Ω. However, a path must be
provided for the input bias current of both inputs. This input bias current is approximately ±5 nA. High input
impedance means that this input bias current changes very little with varying input voltage.
Input circuitry must provide a path for this input bias current for proper operation. Figure 28 shows various
provisions for an input bias current path. Without a bias current path, the inputs float to a potential which exceeds
the common-mode range of the INA118, and the input amplifiers saturates.
If the differential source resistance is low, the bias current return path can be connected to one input (see the
thermocouple example in Figure 28). With higher source impedance, using two equal resistors provides a
balanced input, with the possible advantages of lower input offset voltage due to bias current, and better highfrequency common-mode rejection.
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Typical Application (continued)
Microphone,
Hydrophone
etc.
INA118
47kΩ
47kΩ
Thermocouple
INA118
10kΩ
INA118
Center-tap provides
bias current return.
Figure 28. Providing an Input Common-Mode Current Path
9.2.3 Application Curves
1-kHz differential signal is also present but cannot be seen in this
waveform.
Figure 29. Input of Typical Application Showing 60-Hz
Common-Mode Signal
Figure 30. Output of Typical Application Shows Desired
1-kHz Waveform With
Common-Mode Interference Rejected
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10 Power Supply Recommendations
10.1 Low-Voltage Operation
The INA118 can be operated on power supplies as low as ±1.35 V. Performance of the INA118 remains
excellent with power supplies ranging from ±1.35 V to ±18 V. Most parameters vary only slightly throughout this
supply voltage range; see Typical Characteristics. Operation at low supply voltage requires careful attention to
assure that the input voltages remain within their linear range. Voltage swing requirements of internal nodes limit
the input common-mode range with low power supply voltage. Figure 3 shows the range of linear operation for a
various supply voltages and gains.
V+
–
VIN
+
RG
VO
INA118
10.0V
6
REF102
Ref
R1
1MΩ
C1
0.1µF
R1
2
R2
4
Pt100
1
f–3dB =
2πR1C1
OPA602
Cu
K
= 1.59Hz
Cu
RG
Ref
R3
100Ω = RTD at 0°C
ISA
TYPE
Figure 31. AC-Coupled Instrumentation Amplifier
–
VIN
R1
RG
IO =
INA118
MATERIAL
COEFFICIENT
(µV/°C)
R1 , R 2
E
+ Chromel
– Constantan
58.5
66.5kΩ
J
+ Iron
– Constantan
50.2
76.8kΩ
K
+ Chromel
– Alumel
39.4
97.6kΩ
T
+ Copper
– Constantan
38.0
102kΩ
Figure 32. Thermocouple Amplifier With Cold
Junction Compensation
VIN
•G
R1
2.8kΩ
LA
+
RG/2
RA
Ref
VO
INA118
VO
INA118
Ref
IB
2.8kΩ
G = 10
390kΩ
A1
IO
Load
A1
IB Error
OPA177
OPA602
OPA128
–1.5nA
–1pA
–75fA
Figure 33. Differential Voltage to Current Converter
18
1/2
OPA2604
RL
1/2
OPA2604
10kΩ
390kΩ
Figure 34. ECG Amplifier With Right-Leg Drive
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10.2 Single-Supply Operation
The INA118 can be used on single power supplies of 2.7 V to 36 V. Figure 35 shows a basic single supply
circuit. The output Ref terminal is connected to ground. Zero differential input voltage demands an output voltage
of 0 V (ground). Actual output voltage swing is limited to approximately 35-mV above ground, when the load is
referred to ground as shown. Figure 15 shows how the output voltage swing varies with output current.
With single supply operation, V+IN and V–IN must both be 0.98-V above ground for linear operation. It is not
possible, for example, to connect the inverting input to ground and measure a voltage connected to the
noninverting input.
To illustrate the issues affecting low voltage operation, consider the circuit in Figure 35, which shows the INA118
operating from a single 3-V supply. A resistor in series with the low side of the bridge assures that the bridge
output voltage is within the common-mode range of the amplifier’s inputs. See Figure 3 for 3-V single supply
operation.
+3V
3V
2V – DV
RG
300Ω
VO
INA118
Ref
2V + DV
150Ω
R1 (1)
NOTE: (1) R1 required to create proper common-mode voltage,
only for low voltage operation — see text.
Figure 35. Single-Supply Bridge Amplifier
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11 Layout
11.1 Layout Guidelines
TI always recommends paying attention to good layout practices. For best operational performance of the device,
use good printed-circuit-board (PCB) layout practices, including:
• Take care to ensure that both input paths are well-matched for source impedance and capacitance to avoid
converting common-mode signals into differential signals. In addition, parasitic capacitance at the gain-setting
pins can also affect CMRR over frequency. For example, in applications that implement gain switching using
switches or PhotoMOS® relays to change the value of RG, select the component so that the switch
capacitance is as small as possible.
• Noise can propagate into analog circuitry through the power pins of the circuit as a whole, and of the device
itself. Bypass capacitors are used to reduce the coupled noise by providing low-impedance power sources
local to the analog circuitry. Connect low-ESR, 0.1-μF ceramic bypass capacitors between each supply pin
and ground, placed as close to the device as possible. A single bypass capacitor from V+ to ground is
applicable for single-supply applications.
• Separate grounding for analog and digital portions of the circuitry is one of the simplest and most effective
methods of noise suppression. One or more layers on multilayer PCBs are usually devoted to ground planes.
A ground plane helps distribute heat and reduces EMI noise pickup. Make sure to physically separate digital
and analog grounds, paying attention to the flow of the ground current. For more detailed information, see
Circuit Board Layout Techniques (SLOA089).
• To reduce parasitic coupling, run the input traces as far away from the supply or output traces as possible. If
these traces cannot be kept separate, crossing the sensitive trace perpendicular is much better than in
parallel with the noisy trace.
• Keep the traces as short as possible.
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11.2 Layout Example
Gain Resistor
Bypass
Capacitor
RG
RG
VIN
V-IN
V+
VIN
V+IN
VO
V-
Ref
-
+
V+
VOUT
GND
Bypass
Capacitor
V-
GND
Figure 36. Layout Recommendation
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Development Support
Table 1. Design Kits and Evaluation Modules
NAME
PART NUMBER
TYPE
DIP Adapter Evaluation Module
DIP-ADAPTER-EVM
Evaluation Modules and Boards
Universal Instrumentation Amplifier Evaluation
Module
INAEVM
Evaluation Modules and Boards
Table 2. Development Tools
NAME
PART NUMBER
TYPE
Calculate Input Common-Mode Range of
Instrumentation Amplifiers
INA-CMV-CALC
Calculation Tools
SPICE-Based Analog Simulation Program
TINA-TI
Circuit Design and Simulation
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation, refer to the following: Circuit Board Layout Techniques
12.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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6-Feb-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
INA118P
ACTIVE
PDIP
P
8
50
Green (RoHS
& no Sb/Br)
NIPDAU
N / A for Pkg Type
-40 to 85
INA118P
INA118PB
ACTIVE
PDIP
P
8
50
Green (RoHS
& no Sb/Br)
NIPDAU
N / A for Pkg Type
INA118U
ACTIVE
SOIC
D
8
75
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
INA118U/2K5
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
INA118U/2K5G4
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
INA118UB
ACTIVE
SOIC
D
8
75
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
B
INA118UB/2K5
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
B
INA118UBG4
ACTIVE
SOIC
D
8
75
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
B
INA118UG4
ACTIVE
SOIC
D
8
75
Green (RoHS
& no Sb/Br)
NIPDAU
Level-3-260C-168 HR
INA
118U
INA118P
B
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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